Abstract Detail

The investigation on protein evolution of Y chromosome in Carica papaya.

The sex chromosomes in Carica papaya are a good model to study the early stages and dynamics of sex chromosome evolution due to their relative recent formation. While the structure of sex chromosomes in papaya has been greatly studied in recent years, the role of selection and/or other evolutionary mechanisms that may affect their formation is still unclear. Previously, DNA polymorphism and divergence in noncoding sequences of four X/Y- linked gene pairs showed a high polymorphism level on the Y chromosomes relative to the X which is unexpected under recombination cessation of Y chromosome. This indicated a different evolutionary mechanism working on the nascent sex chromosomes in papaya than in other sex chromosome systems. Here we focus on protein-coding sequence variation will present direct evidence on the role of selection on functionally-relevant mutations. Sequencing results of six X/Y-linked gene pairs are being analyzed by molecular population. These six genes are all in a region (~1 Mbp on the Y with only eleven genes) containing the female-suppressing sex determining locus. At the same time, comparative analyses on the coding sequences of all genes across non-recombining region will be expected to infer impaired adaptive evolution on most Y-linked genes. We propose to find the cues and signature of specific sex biased genes on the Y chromosome, as well as to distinguish different adaptive evolution rates in Y-linked genes relative to the X homologues. The results of this study will be helpful in understanding the history in the evolution of incipient Y chromosome in papaya.